Automatic burner control system



y 27, 1943- R. s; CRAIG 2,325,229

AUTOMATIC BURNER CONTROL SYSTEM Filed June 18, 1941 A! 32 IGN.

INVENTOR Roberi" Craig ATTORNEY Patented July 27, 1943 I I 2 3 5 2 UNITED STATES, PATENT OFFICE: I 2,325,229 1;;v 1 .7

AUTOMATIC BURNER CONTROL SYSTEM Robert S. Craig, Robbinsdale, Minn., assignor to Minneapolis-Honeywell Regulator" Company, H q Minneapolis, -Minn., a corporation of Delaware Application June 18, 1941, Ser ial No; 1398,6111 v 3 in 5 4 1 Y .7 This invention relates generally toautomatic of blades2liand 2il will beincapablbor" returning systems for controlling fuel burners and is more switch blade ,lflftogclosed circuit position: This particularly concerned with simplewand inexmust be accomplishedv manually by the trip free pensive systems in which'a. timed trial ignition reset memberlS. The safety switch II has been period as well as protection against flame failure illustrated more, or less diagrammatically and are necessary. may take any one of'many forms. One of the One of the main objects of the present invenforms which this device may take is illustrated tion is to provide a system which employs, the in the patenttto Miller,N0. 2,237,262. usual thermally timed safety switch, a two wire Illustrated atjZlis a conventional type-of comcombustion switch, and anelectrical means for in 'bustion responsive switch WhiChfiS closed-cold. controlling the fuel feed, wherein the parts are This, switch is shownas comprising aswitch-arm so arranged that the scavenger period is timed v 28 which cooperates with, a stationary, contact by the combustion responsive'switch, and the .29, and for the'purposes ofv illustration is,shown system checks itself each cycle for a burned out as being actuated ,by means of a bimetal'helix 3t, heater for the thermal timer. In addition, the :Itfis customary-to connect the helixfill'with the system is so designed that it will open the safety switcharrnt'zfl through a slipfriction connection switch a predetermined time after a dame failso that theswitch arm willbevactuated upon'a ure andwill therefore not recycle. I v. reversalintemperature change rather than upon These and other objects will readily become the attainment/of, any-predeterminedtempera apparent as the following specification is read 20 ture. Itwill be appreciatedthat anyotherrorm in the light of the accompanying drawing .in of combustionresp'onsiveswitchmay be substiwhich the single figure illustrates schematically ,tuted for the device illustrated. i an oil burner control system embodying my in- The/control system is intended to control the vention. Although this system will'be described 'usual type of oil burner motor, indicated at 32 as an oil burner control system, it will readily c2 and the oil deliveredtothe combustion chamber be appreciated that this invention may-be adaptof thes-furnace by thismotor is to beignited by ed for use in systems controlling variousother means ofan ignition-device. l t types of fuel. i Y I l ozylndic'ated at. is a relay winding which is Referring now to thedrawing; the reference adaptedgtogcontrolswitch arms4l. and G2 which numeral l0 indicates generally thevusual typeof J cooperate respectively with stationary contacts room thermostat comprising a bimetallic ele- 43 and. Whenthe relaywinding is energized ment 1 l which is fixed at oneend and which carthe switchzarms are moved into engagement with ries at its free end a pair of resilient contact their stationary contacts, and when'the-winding blades l2 and'l3 which cooperate'respectively is deenergized these arms move out of engage? with stationary contacts l4 and 15. v The blades :3; ment with the:station'arycontacts through; a biand contacts are so arra ed that on a decrease asing springsorby-means of gravity.

in temperature the contact blade l2 will first Electricalpower is-suppliedto. the controlsys engage contact I4 and at a slightly lower temtem by means of -the line wires 34 and -35, which Perature the contact bladel3 will engage 00 feed the primary winding 36 ofua step dow'n tactl5.

, 1 r 0 transformer 31"bylme'ans otconductors 38 and Indicated generally, at I! is a-safety'switch 39. I 1 n 7 l v ;v which comprises a pair of resilient contact blades 3 Operati'o'nl8 "and 19 which are biased to open'circuit posi- Y 1 tion but which are normally held closed byfmeans 4 2i stat s?trt;ctrztltztaaar m h nc a which in turn is connectedto the bimetallic blade Q t P 1 an '3 a i i?- iz t 22 one as or which isfixed. The blades 20 and W173?! 'v-r i s na y con ac s and 2| are adapted to be heated'by-means of an .5 T W1I111I1g 0 W111 thereforebe deelectrical heater :3, which upon being energized J50 zed and ecqg a m 4' @4 42 W111 be causes the blades 20 and2l towarp in adirection 111 91 vrposltlon anrbthe burner motor tomove the upper end of=the blade 2!];from be- .73 and gnit on dev ce 33 w ll LP? deenerg zed'. neath the flexible contact blade I 9 and permit Combust on will notvbepresent mlthg g mg g it to move to openrcircuitx position. After this and therefore thesw tch arm 2i3 11:b m em action has once taken place, asubsequent cooling 5 5 gagement with rt statyqnayy 99m??? 112 The partsifare s'hown in the "drawingin 3 the position. which they will. assume, whenthe' room ate efiect upon the system due to the fact that the contact arm 4| is in open circuit position. A further decrease in room temperature will cause f contact blade I3 to engage its stationary contact 15. This will establish a circuit for the relay winding 40 which may be traced'asfollowsi from one side of the secondary winding4i of the transformer 31, through conductor 41, stationary con- -ducticn is current, however, is not sufficient to drop out the relay 40 and therefore the burner motor 32 and ignition device 33 remain energized. In addition to reducing the current flow through the heater 23 which is heating the thermal .blades and 2|, the heater 66 heats thermal blade 22 which is so arranged that on an increase in temperatureit warpsina direction to maintain the free end of thermal blade 20in latching engagement with the switch blade [9. In fact,

this thermal blade 22 is the usual compensating blade for the thermal safety switch which norman compensates it for variations in ambient temperature. Therefore, if the blade 22 is heattact 14, contact blades l2 and-l3, contact 15,

conductor 48, relay winding 40, conductor 49,

contact 28, switch arm 28, conductors 50 and 5|,

heater 23, conductor 52', switch blades 18 and I9, and conductor 53 back'to the otherside of the secondary winding 46.- The above-circuit will cause energiz'ation of both the relay'winding 40 and theelectric heater-23 for the safety' switch. Energizationbfthe safety'switch heater- 23 ,will

cause the thermal blades" and-2| 'to' warp in a direction to trip' the safety switch blade 19' to open circuit position. Energization of the relay winding 40 will cause switch arms and 42 to engage their stationarycontacts 43 and 44. Switch arm closes a holding circuitfor the relay winding 43 which is independent of switch blade I3 and contact I51 Thisclrcuit'may be traced from-one side of the secondary winding 48 through conductor 41, contact l4, switch blade l2, bimetal' ,conductor 55, contact 43, switch arm 41, conductor-56, relay winding 40, conductor 49, contact 29, switch arrn'fl, conductors SI and 5 I heater 23, conductor 52, contact blades l8 and I9, and conductor, back-t0 the other side of the secondary winding46. 1 I

Engag'ementof contact arm 42 with the contact 44 establishes a circultfrom line wire 34 through conductor 58; switch armfl, contact 44-, conductors 59 and 60, burner'motor 32, and conductor 6| back to the other line wire 35.- 'J'Ihis connects the burner motor 32 across the two line.

wires 34 and and hence causes itsenergizationfi The'ignitlon device 3315 connected. in parallel with the 'bumer motor 32 by the conductors-G2 and Hand hence theignition device is energized simultaneously with the: burner motor 32. i

' If combustion is not established; the thermal blades 2|! and 2| willcontlnue to heat and will after a predetermined period of tim permit switch blade l9 to move to open circuit position. As set forth above, this blade cannot be returned to closed circuit position without the-manual operation of the reset member 25. Normally, howevein'when the burner motor 3 and ignition 'device, 33 are energized, combustion will take. place. in response to theestablishment of combustion, the combustion responsive switch arm 28 will separate from its stationary contact 2.9,.thus breaking theoriglnal energizing circuit for the relay winding and the electric heater It will be noted, however, that there is a shunt circuit around the combustion responsive switch 28,29. 'This'circu'it comprises conductor 55, electric heater Stand conductor Bl. The ciruit' for the relay winding and theelectric heater 23 now, includes therefore the currentflo'w is reduced. This reed to thesam'etempe'rature as the blades 20 and 1| ,"th e free end or the blade 20 will occupy the mal elements are cold. Therefore energization of the heater 65 prevents the heater 23 from causing the thermal blades 20 and 2| from opening'the' safetytswitch-li;19;:

On an increase in room temperature, the switch blade M will separate from contact 15. This will have no'effect upon thev system due to the holding circuit for the relay winding 40 which passes through switch arm 4! and contact, 43. .With a further increase in' room. temperature the switch blade i: will separate from-contact I4 and deenergize the relaywinding. aswell as .both of theelectricheatersi23-and 66. This will re:- sult in a complete deenergization of the system.

The resistance values of the two heaters 23 and 55 are so chosemthat should the two resilient .due to a powerfailnrea If a flame failure should'occur when the system is in running condition, the switch arm 23 will be moved into engagement with its;contact 29 thereby shuntingthe electric heater; This will effectively deenergize thisheater and will increasethe -.energizat ion'of the heater23 and after aprdgtfirmined period of time ,the thermal blade 20 will move from beneath contact blade 19, whereupon-this blade-will moveto open circuitiposition and the system will be effectively lockedout. g

"It will therefore be seen that I have designed a system whichis relatively simple; and inexpensive in that it utiiizes a single -relay,-a two wire combustion switch, and a safety switch and yet one whichwil'l protectiagainst a momentar y power failure bYEiIItGIPpQSlllQ a scavenging period before the burner I motor can; be reenergized and onewhich will check itself each cycle for a burned out safety switch heater. Thislast result isob- ,tained-becauseif the heater 23, burns out at :any

time the circuit to the relay; winding lll-wil-l be T'brekenyand' hence the burner motor and ignition wentlon may 'occur'to those who are skilled ,in the theelectric heater and e art, and I thereforeiw lshitrto;bee-understoo that I intend to 'be'lmflted thecscope of the-b s pended claims and not b the specific embodiment disclosed.

I claim as my invention:

1. A fuel burner control system comprising in combination, an electrical fuel feeding device, an electrical relay in control thereof, a thermal timer com in an actuating thermostat and a compensating thermostat, a first heater for said actuating thermostat, a second heater for said compensating thermostat, a closed cold stack switch continuousiy connected in shunt with said second heater, a main switch, and an energizing circuit for pulling in said relay comprising said main switch, stack switch and first heater, ener-- gization of said first heater causing said actuating thermostat to deenergize said electrical fuel feeding device after a predetermined period of time, the establishment of combustion causing said combustion switch to open'thereby energizing said second heater to prevent said actuating thermostat from deenergizing said fuel feeding device, said secondheater having an impedance such that said relay can be held in but not pulled in when said combustion switch is open.

2. A fuel burner control system comprising in comb'niation, an electrical device in control of fuel feed, a thermal timer for controlling the energization of said device comprising an actuating temperature responsive device and a compensating temperature responsive device, a first electrical heater for said actuating temperature responsve device, a second electrical heater for said compensating temperature responsive device,

bustion switch, and said first heater, said thermal timer being eifective upon the continued enere ing temperature responsive device and a com-,

pensa-ting temperature responsive device, a first electrical heater for said actuating temperature responsive device, a second electrical heater for said compensating temperature responsive device, a a main control switch, combustion responsive means includin a closed cold combustion switch,

' an energizing circuit forsaid device including a main control switch, combustion responsive means including a closed cold combustion switch, an energizing circuit-for said device including said main control switch, said cold closed comsaid maincontrol switch, said cold closed combustion switch, said safet switch, and said first heater, said safety switch being efiective upon the continued energization of said first heater alone to open and cause deenergi'zation of said electric device, and circuit connections continuously connecting said second heater across the terminal of said closed cold combustion switch so that upon said combustion switch opening in. I response'to the establishment of combustion, said first and second heatersare effectively connected in series in said energizing circuit. a

ROBERTS. CRAIG.

series in said energizing 

